1. Field of the Invention
The present invention relates to a dilatation catheter for use in medical procedures such as PTCA (i.e., Percutaneous Transluminal Coronary Angioplasty) operation and the like, the catheter also being used for dilatation (i.e., widening in diameter of the passageway) of a stenotic lesion of a tubular organ such as blood vessels and the like.
2. Description of the Prior Art
When a deposit called atheroma appearing in an inner peripheral wall of a coronary artery through which the blood is supplied to the heart muscles grows in gravity, i.e., a so-called atherosclerosis becomes serious, the amount of the blood to be supplied to the heart muscles decreases, which increases the potential for angina pectoris or cardiac infarction.
In order to cure the atherosclerosis, a drug is administered. In addition to this, in case that the disease is serious, the PTCA, i.e., operation for dilatation of the coronary artery is conducted.
In the PTCA, as shown in FIG. 8, a pipe-like guiding catheter 100 is introduced from the root of a patient's thigh into his body to have its tip portion reach an coronary inlet portion 301 of a coronary artery 300 through a cardiac aorta 200 and engage with the inlet portion 301. A catheter assembly 1, which is provided with a balloon 11 in its front-end portion, is introduced into the patient's body by using a guide wire 500 through the guiding catheter 100. Then, at first, a front-end portion of the guide wire 500 is passed through the coronary inlet portion 301 and a stenotic lesion 400 of the coronary artery, and temporarily fixed there. After that, the catheter assembly 1 is followed to the guide wire 500 and introduced into the coronary artery 300 from its inlet portion 301 to reach the stenotic lesion 400 of the artery 300 so that the balloon 11 is located in the stenotic lesion 400. Under such circumstances, the balloon 11 is inflated with a radiopaque dye to exert an expanding pressure on the stenotic lesion 400 of the coronary artery 300, in which the deposit called atheroma is located, so that the stenotic lesion 400 is forcibly opened to allow the blood to pass therethrough.
More specifically, the catheter assembly 1 is constructed of the balloon 11 in distal-end portion, a hub in proximal-end portion, an outer tube and an inner tube which is provided inside the outer tube in a condition in which the inner tube has its tip portion projected outward from the outer tube. The balloon 11 has a front and a rear opening portion thereof fixedly mounted on an outer peripheral surface of the inner tube and that of the outer tube in the vicinities of front-end portions of these tubes, respectively. The balloon 11 is made of PE (i.e., polyethylene) resins or PET (i.e., polyethylene terephthalate) resins to assume a thin-walled one. In use, the balloon 11 wrapped around the inner tube of the catheter assembly 1 is under negative pressure and inserted into the guiding catheter 100 in its wrapped condition.
However, the inner tube made of plastic resins and provided with the balloon 11 is too small in diameter, and, therefore tends to be kinked at the same portion in operation when it is passed through a bent portion of the guiding catheter 100 or that of the coronary artery 300 or when it hits against the stenotic lesion 400, which makes it hard for the inner tube of the catheter assembly 1 to pass through the stenotic lesion 400. Further, there is a fear that the coronary artery 300 and the stenotic lesion 400 are damaged to cause a fatal accident during the above operation. In order to avoid such accident, the catheter assembly 1 is frequently replaced with a new one in the same operation, which takes to much time and labor.
After completion of the operation, the catheter assembly 1 is pulled out of the guiding catheter 100 in a condition in which the balloon 11 is deflated by drawing off the radiopaque dye.
However, in case that the balloon 11 is made of PET (i.e., polyethylene terephthalate) resins, when the balloon 11 is deflated, it assumes a flatfish-like shape having a wide slightly larger than a diameter of the inflated balloon 11 without shrinking in size due to its poor resiliency in contrast with PE (i.e., polyethylene) resins. Such flatfish-like shape of the deflated balloon 11 makes it sometimes hard to pull the balloon 11 out of the guiding catheter 100 due to frictional resistance therebetween, and even makes it impossible to push and pull the catheter assembly 1 in the coronary artery 300, which may damage an inner wall of the coronary artery 300 and also damage the balloon 11 in an inlet portion of the guiding catheter 100.